This project will characterize early rhythmic behaviors from home videotapes of children later diagnosed with autism or mental retardation. It is hypothesized that rhythmic behaviors, which normally occur with high frequency during infancy, are related to later abnormal stereotyped and self-directed behaviors. Stereotypy scores derived from direct observations at 1 and 2 years of age will be compared to similar direct observational measures and global assessments of stereotypy using contemporary measures (e.g. the CARS) obtained at 3-4 years of age. Stereotypy scores in the first and second year of life will also be compared to measures of general cognitive function and performance on specific neurocognitive tests at 3-4 years of age. This study will specifically: (1) characterize the stability of different stereotypic (rhythmic) behaviors at one-year intervals between the ages of one and four years; (2) identify early temporal and topographic characteristics of stereotypic behaviors that are expected to predict the development of later abnormal behaviors; and, (3) determine which features of early stereotypies (intensity, frequency, topography) predict lower cognitive functioning. Stereotyped and self-directed behaviors, seen in many individuals with mental retardation or mental illness, pose serious problems for individual safely, quality of life, and financial costs for care. Despite considerable research aimed toward elimination of these behaviors, the problem continues to be one of the most serious predictors of chronic institutionalization, morbidity and premature death in individuals with developmental disorders. There is neither an understanding of the development of stereotypies and self-directed behaviors nor an ability to predict which individuals within these populations will develop these debilitating behaviors. These studies ultimately aim to identify specific early predictors of self-directed behaviors, thus permitting earlier and informed intervention in high- risk child populations with severe developmental disorders.